Query classifier ignored implicit commits in cases of write commands. Fixed it.

Added more tests for transaction support. Mostly different cases where some command triggers implicit commit in the middle of transaction.

server/modules/routing/readwritesplit/test/test_implicit_commit3.sql

@@ -0,0 +1,9 @@
+USE test;
+DROP TABLE IF EXISTS T1;
+SET autocommit=0;
+BEGIN;
+CREATE TABLE T1 (id integer); -- implicit commit
+SELECT (@@server_id) INTO @a;
+SELECT @a; --should read from slave
+DROP TABLE IF EXISTS T1;
+COMMIT;